For those that don't believe in the negative effects of closely
coupled trace meanders, I have done some Hspice simulations.
For the purposes of this discussion a single trace trombone
is used for the meander.

The trace characteristics are as follows:

microstrip
width = 5 mil
height = 4 mil
Er = 4.2

Here is the maxwell matrix used for a single uncoupled
microstrip trace:

Z0 =
54.893028
L =
3.3446803e-007
C =
1.109993e-010
R =
4.1015467

Here is the maxwell matrix for coupled microstrip
with 5 mil seperation:

Note that for 5 mil track to track seperation there is
substantial mutual coupling. This coupling translates
into crosstalk across the meander.

Discussion:
A trace meander is no different than two coupled sections
of trace. As a wave enters the meander, track to track
mutual capacitive and inductive coupling cause energy to
be removed from the primary trace and placed on the secondary
causing forward and reverse crosstalk. This effect is observed
as an apparent reduction of the characteristic impedance of
the primary trace.

When the primary wave reaches the end of the trombone
in the meander, a much more complex interaction of the primary
wave and the forward crosstalk wave in the secondary track
occurs, causing a large dip in the voltage for the pulse width
of the negative going forward crosstalk, as the primary wave
"turns the bend." This is easily misinterpreted in a TDR as
a funky end effect due to corners. In fact, it is just the superposition
of the forward primary wave and the forward crosstalk wave on
the meander.

After the primary wave "turns the corner" There is now energy being
transferred back to the first trace in the meander. Again lowering
the apparent impedance.

At this point there are a bunch of forward and reverse crosstalk
waves "floating around" across the meander. It gets a bit too
complicated for this little brain of mine to keep track of. Thank
God for simulators.

The attached HSpice simultation of a 1ns long meander section
shows these effects, plus some others.

Should one want to simulate this test case, I have also included
an HSpice deck for the enjoyment of all concerned.

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